Earlier versions of this research were presented at the 2007 and 2008 annual meetings of the International Studies Association, Chicago and San Francisco; a 2007 PIPES workshop at the University of Chicago; the 2005 annual meeting of the Peace Science Society, Iowa City; and the 2005 annual meeting of the American Political Science Association, Washington, DC. The authors thank Jesse Johnson, Shireen Nasir, Ashwan Reddy, Patricia Restrepo, and Alice Tsao for research assistance, Zachary Elkins and Tom Ginsburg for sharing data, and Terry Chapman, Giacomo Chiozza, Joe Clare, Barbara Geddes, Hein Goemans, Marc Kilgour, Stephen Long, Lanny Martin, Cliff Morgan, Jim Morrow, Bill Reed, Burcu Savun, John Stevenson, Randy Stevenson, Mike Tomz, Greg Vonnahme, and seminar participants at PIPES and the University of Texas for helpful advice. Portions of this work were completed while Leeds was serving as a Campbell National Fellow and Susan Louise Dyer Peace Fellow at the Hoover Institution at Stanford University. Data for replication are available at http://www.ruf.rice.edu/~leeds.